Adaptive servo control of an optronic sight

Abstract

The invention relates to an optronic sight (2) for a motorized vehicle such as an aircraft, marine or land vehicle, comprising a sighting module (4) capable of being moved around a first axis (8a) and a second axis (10) not parallel to the first axis (8a), - means for moving (17a, 17b) the sighting module around the first (8a) and the second axis (10), - means for continuously measuring an angular data of said module (4) around the first and second axes, characterized in that it comprises a servo loop including: - means for acquiring the fundamental frequency of vibratory disturbances generated by the operation of at least one device of the sight, and - an adaptive controller (26) configured to receive as input: - said fundamental frequency, - a difference between an angular setpoint value (yck) and said angular data - to provide as output a setpoint value for movement to the movement means (17a, 17b).Figure to be published with the abbreviation: Figure 3.

Description

Title of the invention: Adaptive servo control of an optronic sight. Technical field of the invention

[0001] The present invention relates to the control of an optronic sight for a motorized vehicle such as an aerial, marine or land vehicle. Prior art

[0002] With reference to Figures 1 and 2, which illustrate an optronic sight and an operating diagram of such a sight according to the prior art, an optronic sight 2 consists of a set of cameras and / or a pointing device, called a sighting module 4. This sighting module 4 is placed on a support 6 of a motorized vehicle and can move along two axes 8a, 10. The line of sight 12 of said optronic sight 2 designates the optical axis extending from one of these sensors. The purpose of the optronic sight 2 is to orient the line of sight 12 towards a target regardless of the movements of the motorized vehicle and / or the target, and regardless of the external environment (atmospheric conditions, etc.). To this end, said sighting module 4 includes means 14 for continuously measuring an angular data, i.e.a gyrometer in the case of measuring angular velocity or a gyroscope to measure the angular position of the line of sight 12, as illustrated in [Fig.1]. .

[0003] The carrier vehicle, by its movements or motorization regimes, generates angular disturbances which degrade the stabilization of the line of sight 12 of the optronic sights 2. It is therefore necessary to implement a process allowing the image to be stabilized precisely and therefore in particular to correct the angular data (speed or angular position) of the line of sight 12 by means of a corrector 15. This correction is then done by means of control means 16 of the movement means 17a, 17b which may include gimbals actuated by motors.

[0004] To reject the vibrational disturbances acting on the sighting module 4 and thus make the sighting line 12 fixed in an inertial frame, it is therefore necessary that the sum of the torques, i.e. the motor torque Cmot, the torque due to the disturbances and the friction torque Cfd due to the cardan bearings, applied to the sighting module 4 be zero.

[0005] For this purpose, it is conventionally known to use a servo loop 20 capable of acting on the angular data (velocity or position) of the line of sight 12 as illustrated in [Fig. 2]. Each block of said servo loop 20 can be designed as a system, that is to say, a set of relations linking inputs and outputs that can be made explicit using transfer functions.

[0006] The purpose of the control loop 20 is therefore to allow the motors to generate a torque Cmot which compensates, in particular, for the friction torque Cfau at the motorized gimbals in order to stabilize the angular orientation of the line of sight when a carrier vehicle carrying the sight moves angularly. This is referred to as the transfer function Hmot between a voltage u and a torque Cmot. The setpoint u of the motors is generated by the output of a controller K. This control loop aims to make the output y tend towards a reference yck, even though the motors and gimbals are subject to disturbances due to the gimbal rolling Cf and the angular disturbance <5V.

[0007] The line-of-sight control function of the optronic sight 2 comprises an analog part 22 and a digital part 24. First, in the analog part 22, the spectral lines associated with the disturbing vibrations Vvib generated by the rotation of the rotor and blades of a helicopter are identified, and fixed filters on these spectral lines are subsequently created. Thus, the transfer function Hvib makes it possible to model the impact of the disturbing vibrations Yvib on the angular orientation of the line of sight. The output of the transfer function therefore provides the angular perturbation of the line of sight due to the disturbing vibrations Yvib, which can then be considered in the control loop of the optronic sight. This control method is therefore based on prior knowledge of a model of the system under study.

[0008] Next, another step consists of modeling the dynamics of the measurement of the angular data (position or angular velocity) of the line of sight using a transfer function called Hgyro. This transfer function is based either on the measurement y of the position of the line of sight via a gyroscope, or on the measurement y of the angular velocity of the line of sight obtained by a gyroscope, or more precisely by the inertial sensor of the gyroscope. The measurement of the angular data of the line of sight obtained, ym, then passes through an Analog-to-Digital Converter (ADC) and is thus sampled to become the sampled measurement ymk. A control error Σk is then obtained by subtracting the sampled measurement ymk from a reference yck. This control error then passes into the input of a linear and time-invariant controller K.The latter is calculated to compensate for disturbing vibrations whose fundamental frequency is fixed over time. The software implementation of this compensator K is done as a combination (sum and / or product) of second-order digital linear filters. The output of this compensator is a digital motor control signal uk, which is then transformed into an analog control signal u (voltage) by a Digital-to-Analog Converter (DAC). This analog control signal u is applied to the electric motor. Modeled by the transfer function Hmot, which consequently delivers an electromechanical torque, this allows us to obtain the electromechanical torque Cmot that the motor must supply to rotate the cardan shafts. The larger the error ek, the larger the torque Cmot supplied by the motors must be to reduce this error. The electromechanical torque Cmot supplied by the motor actuates the cardan shafts, modeled by the transfer function Hcardan, in order to compensate for / cancel the error ek. This error is due, on the one hand, to the disruptive torque of friction in the cardan shaft bearings and, on the other hand, to the angular perturbation ôy.

[0009] Furthermore, the optical sight is generally equipped with at least one integrated cooling unit designed to cool the sighting module(s). This is particularly true for sighting modules that incorporate an infrared optical sensor requiring temperature control.

[0010] The cooling machine also generates sinusoidal disturbances whose frequency varies according to the temperature required to cool the aiming module, which itself depends on the temperature of the external environment.

[0011] In the prior art, these disturbances are suffered and are not compensated by the controllers of the servo loop.

[0012] The cold machine is therefore also a source of disturbance for the line of sight, whose natural frequency varies.

[0013] The aim of the invention is therefore to provide an optical sight capable of compensating for disturbances caused by one or more internal on-board disturbance generators that may affect the line of sight. Presentation of the invention

[0014] The invention therefore relates to an optronic sight for a motorized vehicle such as an aircraft, marine or land vehicle, comprising: - a sighting module capable of being moved around a first axis and a second axis (10) not parallel to the first axis, - means of moving the aiming module around the first and second axes,

[0015] - means for continuously measuring an angular value of said modulus around the first and second axes.

[0016] The optical sight further includes a servo loop comprising: - means of acquiring the fundamental frequency of vibratory disturbances generated by the operation of at least one device of the viewfinder, and - an adaptive corrector configured to receive as input:

[0017] - said fundamental frequency,

[0018] - a difference between an angular setpoint value and said angular data - to provide an output value of displacement to the means of movement.

[0019] Thus the adaptive controller varies according to the frequency of the disturbing vibrations by the operation of an on-board device, such as a cold machine intended for cooling an infrared optical sensor, while guaranteeing the stability of the servo loop.

[0020] The adaptive corrector can be connected to said viewfinder device by a digital communication link on which said fundamental frequency of the vibration disturbances is transmitted.

[0021] Advantageously, the communication link is connected to an electronic control module for said sighting device delivering the fundamental frequency.

[0022] The means for continuously measuring said angular data may include a gyroscope capable of obtaining an angular position or a gyrometer capable of obtaining an angular velocity.

[0023] The adaptive controller can be a Linear Controller with Varying Parameters.

[0024] This Linear Variable Parameter Compensator is linear but varies over time, in function of measurable or identifiable parameters. It depends linearly on the varying parameter.

[0025] Said adaptive controller can follow the state representation according to the following formula: fxk+l ^0vk)xk + B0vk)ek l uk = CPvk)xk + $(fvk)ek — ^vk — ^max where xk is the state variable of the controller, is the control error at the controller input, uk is the digital motor control calculated by the controller (controller output), fmin and fmax are two frequencies bounding the fundamental real-time frequency f of the disturbing vibrations Ymàf.

[0026] The Linear Variable Parameter (LPV) controller may include the following affine state matrices: ^(^vk) — Ao+ fvk Ai BPvk) = Bo+ ^vk ^(Jvk) — fvk Cx ^(^vk) ~ fvt Di where Ao, Bo, Co, Do, Ai, Bi, Ci, Di denote matrix gains which are the parameters saved in memory of a software which implements said corrector.

[0027] The first axis and the second axis can be perpendicular to each other.

[0028] The invention also relates to a motorized device such as a helicopter, an aerial, marine or land vehicle comprising an optronic sight as defined above. Brief description of the figures

[0029] [Fig-1] is a schematic view of a prior art optronic sight,

[0030] [Fig.2] is a diagram representing the operation of an optronic sight in earlier art,

[0031] [Fig.3] is a schematic view of an optronic sight according to the invention,

[0032] [Fig.4] is a diagram representing the operation of an optronic sight according to the invention, Detailed description of the invention

[0033] Figures 3 and 4, in which elements identical to those in Figures 1 and 2 bear the same numerical references, respectively illustrate a schematic view of an optronic sight 2 and a diagram representing the operation of such a sight according to one embodiment of the invention. The optronic sight 2 comprises, in particular: - a sighting module 4 capable of being moved around a first axis 8a and a second axis 10 perpendicular to the first axis, - means of movement 17a, 17b of the aiming module 4 around the first 8a and the second axis 10, - means for continuously measuring an angular data of said module around the first 8a and second axis 10.

[0034] In the embodiment illustrated in the figures, the first axis 8a and the second axis 10 are perpendicular, but it is understood that the embodiment details given below are also applicable to embodiments in which the axes are neither perpendicular nor even intersecting. The first axis 8a and the second axis 10 may also be intersecting and not perpendicular.

[0035] The embodiment of figures 3 and 4 is intended to control the position of the optical sight on an angular setpoint value yc and to compensate for the vibrations generated during the operation of internal devices on board the optronic sight, whose fundamental frequency is known or can be estimated.

[0036] This can be any type of device integrated into the viewfinder. However, the described embodiment applies to the compensation of vibrations generated during the operation of a cold machine intended for cooling an infrared optical sensor and whose operation generates vibrations. 'màfV / whose frequency varies according to the machine's operating mode, and therefore depending on the temperature of the machine's environment.

[0037] The position control of the optical sight uses a measurement of the angular data of the line of sight obtained either from the measurement y of the position of the line of sight via a gyroscope, or from the measurement y of the angular velocity of the line of sight obtained by a gyroscope, or more precisely by the inertial sensor of the gyroscope. The dynamics of the angular data measurement (position or angular velocity) of the line of sight is then modeled by a transfer function Hgyro, and the modeled data passes through an Analog-to-Digital Converter (ADC) and is thus sampled to become the sampled measurement ymk. A control error £k is then obtained by subtracting a sampled measurement ymk from a reference yc. This control error £k is then fed into a linear and time-invariant controller K 26.

[0038] Furthermore, the optronic sight 2 of figures 3 and 4 differs from the optronic sight 2 presented with reference to figures 1 and 2 in that, in the servo loop 34 according to the present disclosure, at the input of the corrector K, we now find not only the servo error sk which is a function of the sampled measurement ymk of the angular data but also the fundamental frequency f varying in real time, J vk of the disturbing vibrations Ymàf of the cold machine.

[0039] The adaptive controller K(y) 26 is therefore calculated to compensate for the disturbing vibrations v(f) whose fundamental frequency fvk varies over time according to the operating regime of the device, here the chiller, which generates these disturbances. For this purpose, the excitation frequency of the chiller fJvk, which depends on the regime required to cool the optical sensor, is supplied to the controller by an electronic control module 28 of the chiller via a digital communication link.

[0040] More specifically, the electronic control module of the cold machine provides the controller with an estimate of the fundamental frequency f of the vibrations, this es-J vk timing can advantageously be estimated from the machine's operating regime.

[0041] Regarding the calculations performed by the adaptive controller K(f), three techniques J vk can be used: either by using a Linear Variable Parameter (LPV) control, or by means of a symbolic controller, or by a combination of these two types of controllers (LPV and symbolic).

[0042] In the case of an LPV-controlled controller, a minimal state representation of the system KQ ) is designated by (A, B, C, D) with A e R'ïX”, B e R” xî, C e R1 x" and D t R.. The state-form software implementation of the adaptive controller K( / ) is done according to the following relationship: J vk (xkf 1 — 1 uk ~ ^(^vk)xk + ^(jvk)£k frnin — ^vk — fmax °where xk ER” is the state variable of the adaptive controller, ek is the input control error of the adaptive controller, uk is the numerical control of the means of movement calculated by the adaptive controller (output of the adaptive controller), fmin and fmax are two frequencies bounding the fundamental real-time frequency f of the disturbing vibrations Ymàf. J vk

[0043] The state matrices (A, B, C, D) are affine in / ■ and can be written in the form: J vk APvk) = At BQvk) - 8o+ îvk cPvk) “ Gk ci where Ao, Bo, Co, Do, Ai, Bi, Ci, Di denote matrix gains which are the parameters saved in memory of a software which implements said adaptive corrector K(y).

[0044] Thus the adaptive controller K(y) varies directly as a function of the frequency of disruptive vibrations generated by the on-board device, while ensuring the stability of the control loop.

Claims

Demands

1. Optronic sight (2) for a motorized vehicle such as an aircraft, marine or land vehicle, comprising: - a sighting module (4) capable of being moved about a first axis (8a) and a second axis (10) not parallel to the first axis (8a), - means for moving (17a, 17b) the sighting module about the first (8a) and the second axis (10), - means for continuously measuring an angular data point of said module (4) about the first and second axes, characterized in that it comprises a control loop comprising: - means for acquiring the fundamental frequency of vibrational disturbances generated by the operation of at least one device of the sight, and - an adaptive controller (26) configured to receive as input: - said fundamental frequency, - a difference between an angular setpoint value (yck) and said angular data point - to provide as output a setpoint value for movement to the movement means (17a, 17b).

2. Optronic sight according to claim 1, wherein the adaptive corrector is connected to said sight device by a digital communication link on which said fundamental frequency of the vibration disturbances is transmitted.

3. 3 Optronic sight according to claim 2, wherein the communication link is connected to an electronic control module (28) of said sight device delivering the fundamental frequency.

4. Optronic sight according to any one of claims 1 to 3, wherein the means for continuously measuring said angular data (14) comprise a gyroscope (14) capable of obtaining an angular position or a gyrometer (14) capable of obtaining an angular velocity.

5. Optronic sight according to any one of claims 1 to 4, wherein said adaptive corrector comprises a Linear Variable Parameter corrector.

6. Optronic sight according to claim 5, wherein said adaptive corrector (26) follows a state representation according to the following formula: xk+î - A(îyk)xk + B(îvk)sk . uk ~ ^(^vk)xk + ^(Krk)£k F < î' <' F ^min — lvk — 'max where xk is the state variable of the controller, sk is the input control error of the adaptive controller (26), uk is the numerical control of the means of movement calculated by the adaptive controller (26), fmin and f max are two frequencies bounding the fundamental real-time frequency y of the disturbing vibrations Ymàf.

7. Optronic sight according to claim 5 or 6, wherein said Linear Variable Parameter (LPV) corrector comprises the following affine state matrices: APvk) = Âo+ Kk S(K'k) ~ P'o + ?vk CPvk) = Co+ ?vk C1 ^Gvk) = ^o+ fvk where Ao, Bo, Co, Do, Ai, Bb Ci, Di denote matrix gains which are the parameters saved in memory of said corrector.

8. Optronic sight according to any one of claims 1 to 7, wherein the first axis (8a) and the second axis (10) are perpendicular to each other.

9. Optronic sight according to any one of claims 1 to 8, wherein said sight device is a cold machine for cooling an infrared optical sensor.

10. Motorized device such as an aerial or marine vehicle or a land vehicle comprising an optronic sight according to claims 1 to 9.

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